1. Field of the Invention
The present invention generally relates to image sensing systems and more particularly relates to a circuit architecture and associated method for an image sensor employing an internal mechanism for switching resolutions so as to minimize the number of shift registers in use and increase the overall performance of the image sensor.
2. Description of the Related Art
There are many applications that need an imaging system to convert a target to an electronic format that can be subsequently analyzed, printed, distributed and archived. The electronic format is generally an image of the target. A typical example of the imaging system is a scanner and the target is a sheet of paper from a book or an article. Through the scanner, an electronic or digital image of the paper is generated.
An imaging system generally includes a sensing module that converts a target optically into an image. The key element in the sensing module that converts the target optically to the image is an image sensor comprising an array or matrix of photodetectors responsive to light impinged upon the image sensor. Each of the photodetectors produces an electronic (charge) signal representing the intensity of the light reflected from the target. The electronic signals from all of the photodetectors are readout and then digitized through an analog-to-digital converter to produce digital signal or image of the target.
One very common type of image sensor is a charge coupled device (CCD). Another low cost image sensors, perhaps used more commonly in the future, are made out of complementary metal-oxide semiconductor (CMOS). Generally, a significant number of shift registers are used in both types of the image sensors as auxiliary circuitry to facilitate the readout of the electronic signals. For example, in one type of an image sensor that comprises 1024 (1K) photodetectors, there typically employ 1024 or more shift registers in the image sensor.
It is understood in the art that the area occupied by the large number of shift registers is quite significant compared to the area occupied by photodetectors in a piece of semiconductor that is eventually packaged as an image sensor. The cost of the image sensor would not be further reduced if the size of the image sensor can not be reduced. There is therefore a great need to reduce the size of the image sensor without compromising the overall performance of the image sensor.
CMOS image sensors have many unique characteristics that are being researched to explore possibilities of further performance improvement and cost reduction. One of the desirable possibilities is to determine if the size of a CMOS image sensor can be further reduced while the overall performance is increased. Image sensors of smaller size and improved overall performance will be certainly welcome, especially in consumer electronics markets.